Process of hardening steel.



UNITED STATES PATENT OFFICE.

SHIPLEY NEAVE BRAYSHAVV, OF HULME, MANCHESTER, ENGLAND,

-. ASSlG-NOR TO GEORGE NASH, OF NEW YORK, N. Y.

PROCESS OF H AFlDENlNG STEEL.

Specification of Letters Patent.

Patented Dec. 11, 1906.

I Application filed ne 8, 1906. Serial No. 320,878.

1'0 all juhmn it may concern:

Be it known that I, SIIIPLEY NEAVE BRAY- simw, a sub ect of the King of England, and a resident of llulme, Manchester, county of Lancaster, England, have invented certain new and useful 1m rovements in the Process of Hardening Steel: of which the following is as ecification Q n the ordinary method of hardening ordinary or carbon steel it has been heated in a furnace orotherwise to a certain temperature, known as the hardening-point, which varies according to the composition of the steel, and then quenched in a cold or cool bath of water, Oil, or other liquid. I now find that better results are obtained by heating the steel to a temperature consi erably above the hardening-point and then reducing it to a pointsomewhat below the hardening-point and finally quenching in a cold bath, such as water, brine, or oil. I have discovered that if carbon steel is highly heated a remarkable change occurs at a temperature of about 140 centigrade beyond the hardening-point. This change occurs at what 1 call the hi her change point, and the temperature of this is usually about880 centigrade. If the steel bars are heated to the higher-change oint and then quenched in water, they are ound to be the same length after quenching as they were before the heating began. There are arious other effects due to raisin carbon steel to the higher-change point. For instance, the appearance of the fracture of the steel is a tered very considerably and the value of the steel for many kinds of tools and other articles is enormously iucreased.- I have discovered, further, that after carbon steel has been heated to the higher-change point it may be lowered to a temperature considerably below the ordinary hardening-point, and it will still harden if quenched from this lower temperature. Moreover, it retains many of the roperties which it acquired while it was at t e higher-change point.

I am well aware that carbon steel has frequently been heated up to or above the ordi nary hardening-point and then lowered in temperature below the hardening-point before being quenched and that steel so treated has been hardened; but I find that if steel which has not been heated to the higherchange point is lowered below the ordmary.

hardening point it will soon acquire the condition corresponding to this low temperature, and even a sh rt soaking at this low temperature will bring it into a condition in which it will not harden when quenched. Now after I have raised the carbon steel to the higher-change point I can lower it as much as 20 centigradc (and in some cases a good deal more) below the hardening-point and soak it at this low temperature for a prolonged period, (sometimes as lon as severa hours,) and it will still harden it quenched. I find that when carbon steel is raised to the higher-change point and then lowered to a certain temperature below the hardeningpoint and then quenched in water it hardens without any risk of cracking, and steel which has been hardened in this way possesses valuable cutting and other properties which cannot be given to it by any other means. g

The term carbon steel as I use it in this specification is meant to include carbon steels which contain a small percentage of alloy, and it is used as an antithesis to the term high-speed steel.

In carrying out the invention I beat the articles in a bath at a ver hi h temperature, considerably above the arzIenin -point, so as to reach or pass a certain hig er-change oint. Thus for a steel of which the hardenlug-point is, say, 740 centigrade I should heat up to from 860 to 900 Centigrade. The article is soaked in this bath from a few seconds up to many minutes, according to the size and bulk, until it is uniformly heated up to the full temperature. The article is then removed and i ediately immersed in a sec- 0nd bath (care being taken not to allow it to I cool) at a temperature somewhat below the hardeningointsay about 705 t0-730centigrade. T earticle may besoakedinthissec- 0nd bath for a considerable length of timeabout the same length of time as in the first bath, or until uniformly reduced in temperature to the heat of the second bath. The relative lengths of times, however, for soaking in the two baths are partly dependent upon the temperatures thereof and may be varied considerably. second bath the article is removed and quenched out in a cold bath of water brine. oil, or other liquid, (say about 20 centigrade.) The article may be cold when placed in the first high-temperature bath, or it may be variation in the temperature than formerly;

previously heated in another bath or otherwise; but any preliminary heating must not reach a temperature higher than the temperature of the first bath. Instead of immersing the articles in the first bath for the whole time of heating it sometimes hap ens that I alternately lower them into an lift them out of the bath and keep doing this for and by it I secure an intense hardness of the 5 article so treated, and I find that tools so hardened last much longer and do much more work than any tools previously made of ordi I nary carbon steel.

What I claim as my invention, and desire to protect by Letters Patent, is

1. The process of hardening ordinary carbon steel which consists in heating the article in a bath so as to reach a certain higherchange point at a temperature considerably 45 above t e hardening-point, then soakin it for a considerable time in a bath. somewhat below the hardening-point and subsequently 10 all or part of the time of heating until they a are brought to a temperature uniform with i bath. As a rule' the articles are immersed gonltlinuously for the whole time in the second I: The process may be carried out and the bath heated in a furnace such as that described in the specification of my former patent, N o. 7 69,052 of 1903, or the bath may be heated to the desired degree in any other form of furnace. I prefer the bath to be composed of fused salts; but molten lead or alloy may be used. The temperatures of the baths vary according to the composition of the steel under treatment and also to a slight degree according to the size of the articles under treatment. \Vhen the article has been correctly heated to the high temperature and then lowered as described, there is no risk of brcaka es, even though the temperatures of the haths have varied by an amount that was fatal to the work when it" was hardened at one heat only. This process of [hardening allows a greater range of quenching in a cold bath substantially as de scribed.

2. The process of hardening ordinary carbon steel with a hardening-point of about 740 centigrade which consists in heating in a bath to reach a certain higher-change point at a temperature of 860 to 900 centigrade, then soaking for 'a considerable time in a cooler bath at a tem erature of 705 to 730 centigrade andfinal y quenching in an ordinary cold bath substantially as described.

In witness whereof I have hereunto si ed my name in the presence of two subscrii ing witnesses.

SlIlPLEY NEAYE BRAYSHAW.

Witnesses:

J. OWDEN OBRIEN, H. BARNFATHER. 

